I have from this SA flow, like what is actual attach time.
Is it UE RRC setup request to RRC connection reconfiguration complete?
Or UE RRC setup request to PDU session establishment success?
We we consider re-configuration complete then time is showing around 104 ms.
Really depends what you want to measure.
For instance from user experience perspective simple RRC attach KPI mean little. But RRC + Erab attach means something since that is the point user start getting data.
So you need to check time from RACH or from RRC to last RRC Reconfig complete message after which user start getting service.
From network perspective RRC stage is important KPI and so is rest of attach.
From network monitoring perspective we usually check RRC and ERAB success rates.